Blood sugar could go up because 1) too much sugar intake, 2) less absorption of sugar into cells, 3) less utilization of sugar.
NSF is almost always associated with kidney disease. Kidney disease is a common side effect of diabetes. Many people with NSF have diabetes, or a tendency toward it. So if sugars are going up, it is important to ascertain you do not have diabetes. Diabetes is caused by an inability of cells to take up sugar (glucose). This could be because the insulin necessary to make this happen is not present or not effective. Diabetics also have an impaired ability to make glycogen (see below).
Too much sugar intake? Your body is good at regulating sugar. When too much is present it will be made into glycogen and stored in the liver. Following meals, people ordinarily have an elevation of blood sugar, and depending when the reading (level) was obtained, this might be normal.
Less utilization of sugar: again, if you are not using it, sugar tends to be made into glycogen for later use.
Another effect worthy of discussion: some medications can cause your blood sugar to go up. Commonly used ones include corticosteroids (prednisone), beta-blockers (for hypertension), and thiazide diuretics.
